Process of molding antistatic resin shaped articles

ABSTRACT

A process for the preparation of a synthetic resin-shaped article having good antistatic properties is provided, which entails a) polymerizing a monomer mixture containing monomers (A), (B) and (C) to form a first copolymer; b) subsequently polymerizing monomers (D) and (E) in the presence of the first polymer to prepare a second copolymer; forming a film of the second copolymer on the molding surface of a casting mold; and supplying a starting material capable of forming a synthetic resin into the casting mold and polymerizing the starting material to form the substrate in the casting mold, thereby transferring the film of the previous step to the surface of the substrate from the molding surface of the casting mold.

This is a division of application Ser. No. 07/447,825, filed on Dec. 8,1989, now U.S. Pat. No. 5,093,205.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a synthetic resin shaped article havinggood and permanent antistatic properties, and a process for thepreparation thereof.

2. Description of the Related Art

Currently, the many synthetic resin shaped articles available haveexcellent properties, but in general, since they have a high electricresistance value, they are easily electrically charged by friction orthe like and attract dust and foreign matter to thereby mar theappearance thereof.

As methods of imparting antistatic properties to synthetic resin shapedarticles, there can be mentioned (1) an internal addition of a surfaceactive agent, (2) a surface coating of a surface active agent, (3) asurface coating of a silicon compound, and (4) a surface modification bya plasma treatment. Among these methods, the methods (3) and (4) aredisadvantageous in that the cost thereof is high, and therefore, themethods (1) and (2) are generally adopted.

In the method of an internal addition of a surface active agent, thesurface active agent is incorporated or dispersed in a starting materialfor a synthetic resin before the polymerization, or in a synthetic resinbefore the molding, and therefore the preparation process can besimplified. But to obtain satisfactory antistatic properties, usuallythe amount added of the surface active agent added must be increased,which can result in a lowering of the mechanical strength of thesynthetic resin. Further, the obtained antistatic characteristics areeasily lost by water washing, friction or the like.

The method of surface coating a surface active agent is advantageous inthat the physical properties of a synthetic resin as the substrate arenot affected and good antistatic properties can be obtained by using asmall amount of the surface active agent. Nevertheless, since thesurface coating step is necessary, the cost is increased and there is arisk of a marring of an inherent aesthetically pleasing surface of thesynthetic resin shaped article. Furthermore, the obtained antistaticproperties are easily lost by water washing, friction or the like.

As apparent from the foregoing description, a synthetic resin shapedarticle having good and permanent properties while retaining theinherent physical properties of the synthetic resin has not beendeveloped.

SUMMARY OF THE INVENTION

Under the above-mentioned background, the primary object of the presentinvention is to provide a synthetic resin shaped article having good andpermanent antistatic properties.

More specifically, in accordance with one aspect of the presentinvention, there is provided an antistatic resin shaped article havingimproved antistatic properties which is composed of a synthetic resinsubstrate and a synthetic resin surface layer; at least part of saidsubstrate being covered with said synthetic resin surface layerintegrated therewith; said synthetic resin surface layer being comprisedof a copolymer(a) prepared by the steps of polymerizing a monomermixture comprising (A) more than 20% by weight of a monomer havingquaternary ammonium salt group, which is represented by the followinggeneral formula (I): ##STR1## wherein R₁ represents a hydrogen atom or amethyl group, R₂, R₃ and R₄ represent a hydrogen atom or an alkyl grouphaving 1 to 9 carbon atoms, which may have a substituent, m is aninteger of from 1 to 10, and X⁻ represents an anion of a quaternizingagent,

(B) less than 79.99% by weight of a copolymerizable monomer having oneunsaturatd double bond and (C) 0.01 to 10% by weight of acopolymerizable monomer having at least two unsaturated double bonds, toprepare a copolymer (b) comprising the units derived from the monomers(A), (B) and (C); and further polymerizing (D) 0(exclusive) to 190 partsby weight of a copolymerizable monomer having one unsaturated doublebond and (E) 0(exclusive) to 10 parts by weight of a copolymerizablemonomer having at least two unsaturated double bonds in the presence of100 parts by weight of the copolymer (b) comprising the units derivedfrom the monomers (A), (B) and (C).

In another aspect of the present invention, there is provided a processfor the preparation of the above-mentioned antistatic resin shapedarticle having improved antistatic properties, which comprises the stepsof polymerizing 100 parts by weight of a monomer mixture comprising (A)more than 20% by weight of a monomer having a quaternary ammonium saltgroup, which is represented by the above general formula (I), (B) lessthan 79.99% by weight of a copolymerizable monomer having oneunsaturated double bond and (C) 0.01 to 10% by weight of acopolymerizable monomer having at least two unsaturated double bonds, toprepare a copolymer (b) comprising the units derived from the monomers(A), (B) and (C); subsequently polymerizing (D) 0(exclusive) to 190parts by weight of a copolymerizable monomer having one unsaturateddouble bond and (E) 0(exclusive) to 10 parts by weight of acopolymerizable monomer having at least two unsaturated double bonds inthe presence of 100 parts by weight of the copolymer (b) to prepare acopolymer(a); forming a film of the copolymer(a) on the molding surfaceof a casting mold; supplying a starting material for a synthetic resinas a substrate into the casting mold; and polymerizing the startingmaterial in the casting mold to transfer the film to the surface of thesubstrate from the molding surface of the casting mold.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 illustrates an apparatus for the continuous preparation of amethacrylic resin sheet, which is provided with a device for coating afilm-forming starting material.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The copolymer constituting the synthetic resin surface layer of theshaped article of the present invention is prepared from theabove-mentioned monomers A, B, C, D and E. The monomer A has aquaternary ammonium salt and is represented by the general formula (I):##STR2## wherein R₁ represents a hydrogen atom or a methyl group, R₂, R₃and R₄ represent a hydrogen atom or an alkyl group having 1 to 9 carbonatoms, which may have a substituent, m is an integer of from 1 to 10,and X⁻ represents an anion of a quaternizing agent.

This monomer is obtained by quaternizing an acrylate or methacrylatehaving an amino group with a quaternizing agent. As the acrylate ormethacrylate having an amino group, there can be mentioneddimethylaminoethyl methacrylate, diethylaminoethyl methacrylate,dimethylaminopropyl methacrylate, dimethylaminoethyl acrylate,diethylaminoethyl acrylate, dimethylaminobutyl methacrylate,dihydroxyethylaminoethyl methacrylate, dipropylaminoethyl methacrylateand dibutylaminoethyl methacrylate.

As the quaternizing agent, there can be mentioned alkyl sulfates such asdimethyl sulfate, diethyl sulfate and dipropyl sulfate, sulfonic acidesters such as methyl p-toluenesulfonate and methyl benzenesulfonate,alkyl phosphates such as trimethyl phosphate, and halides such asalkylbenzyl chlorides, benzyl chloride, alkyl chlorides and alkylbromides. From the viewpoint of the resistance to thermal decomposition,an alkyl sulfate and a sulfonic acid ester are especially preferred.Thus, a preferable anion of the quaternizing agent of the monomer (A) isrepresented by the formula R₇ SO₃ ⁻ or R₇ OSO₃ ⁻ in which R₇ representsa hydrogen atom or an alkyl group having 1 to 20 carbon atoms, which maycontain a phenyl group.

In the general formula (I), m is an integer of from 1 to 10, preferablyfrom 2 to 6.

From the viewpoint of the adhesion between the copolymer impartingantistatic properties and the synthetic resin as the substrate,preferably the copolymerizable monomer (B) and/or (D) having oneunsaturated double bond is the same as the monomer used for thepreparation of the synthetic resin substrate or a monomer capable offorming a resin having a good compatibility with the synthetic resinsubstrate.

Known monomers can be used as the copolymerizable monomers (B) and (D)having one unsaturated double bond. For example, there can be mentionedmethacrylic acid esters such as methyl methacrylate and ethylmethacrylate, acrylic acid esters such as methyl acrylate and ethylacrylate, unsaturated carboxylic acids such as acrylic acid andmethacrylic acid, acid anhydrides such as maleic anhydride and itaconicanhydride, maleimide derivatives such as N-phenylmaleimide, hydroxylgroup-containing monomers such as 2-hydroxyethyl acrylate and2-hydroxypropyl methacrylate, nitrogen-containing monomers such asacrylamide and acrylonitrile, and epoxy group-containing monomers suchas allyl glycidyl ether and glycidyl acrylate. Furthermore, there can beused macromonomers such as methacrylate-terminated polymethylmethacrylate, styryl-terminated polymethyl methacrylate,methacrylate-terminated polystyrene, methacrylate-terminatedpolyethylene glycol and methacrylate-terminated acrylonitrile/styrenecopolymers.

From the industrial viewpoint, preferably a compound represented by thefollowing general formula (II): ##STR3## wherein R₅ represents ahydrogen atom or a methyl group, R₆ represents a hydrogen atom or analkyl, aryl or aralkyl group having 1 to 18 carbon atoms, A representsan alkylene group having 2 to 4 carbon atoms, and n is an integer offrom 0 to 500, is used as the copolymerizable monomers (B) and (D)having one unsaturated double bond.

As the compound of formula (II) in which n is 0, there can be mentionedmethyl methacrylate, ethyl methacrylate, butyl methacrylate, laurylmethacrylate, ethylhexyl methacrylate, stearyl methacrylate, methylacrylate, ethyl acrylate, benzyl methacrylate, phenyl methacrylate,cyclohexyl methacrylate and 2-hydroxyethyl methacrylate.

As the compound of formula (II) in which n is an integer of from 2 to500, there can be mentioned polyethylene glycol(4) monomethacrylate,polyethylene glycol(23) monomethacrylate, polyethylene glycol(300)monomethacrylate, polyethylene glycol(23) monoacrylate, polypropyleneglycol(23) monomethacrylate, polybutylene glycol(23) monomethacrylate,polyethylene glycol(23) monomethacrylate monomethyl ether, polyethyleneglycol(23) monomethacrylate monobutyl ether, polyethylene glycol(23)monomethacrylate monostearyl ether, polyethylene glycol(23)monomethacrylate monophenyl ether, polyethylene glycol(23)monomethacrylate monobenzyl ether and polyethylene glycol(23)monomethacrylate oleyl ether (each parenthesized number indicates thenumber of alkylene glycol units in the polyalkylene glycol).

Where the synthetic resin as the substrate is a polymer composed mainlyof methyl methacrylate, if a compound of formula (II) in which n is 0 isused, the adhesion between the synthetic resin as the substrate and thecopolymer imparting antistatic properties is greatly improved, nocopolymer remains on the casting mold upon peeling, and the antistaticproperties can be stably manifested regardless of the kind of castingmold used.

When a compound of the general formula (II) in which n is an integer offrom 2 to 500 is used, the release property of the obtained syntheticresin shaped article from the casting mold, especially the releaseproperty at a high temperature, is improved, and an antistatic syntheticresin shaped article can be stably obtained.

As the copolymerizable monomers (C) and (E) having at least twounsaturated double bonds, there can be mentioned allyl methacrylate,methallyl methacrylate, allyl acrylate, methallyl acrylate, vinylmethacrylate, vinyl acrylate, 1-chlorovinyl methacrylate, isopropenylmethacrylate, N-methacryloxymaleimide, ethylene glycol dimethacrylate,butanediol dimethacrylate, polyethylene glycol dimethacrylate, ethyleneglycol diacrylate, allyl vinyl ether, allylvinylketone,trimethylolpropane trimethacrylate, pentaerythritol tetramethacrylateand triallyl cyanurate.

If one of the functional groups in the monomers (C) and (E) is afunctional group having a poorer polymerizability than the methacryloylor acryloyl group, such as an allyl, methallyl, vinyl, vinylidene orvinylene group, an unreacted double bond remains in the copolymer(a) andcauses graft polymerization at the step of the polymerization forformation of the synthetic resin as the substrate, and therefore, a goodadhesion is obtained between the copolymer imparting antistaticproperties and the synthetic resin as the substrate. This feature alsois preferred in that, at the time of graft polymerization of thecopolymerizable monomer (D) having one unsaturated double bond, thegrafting efficiency is increased to enhance the compatibility betweenthe copolymer imparting antistatic properties and the synthetic resin asthe substrate.

In the present invention, a monomer mixture comprising the monomer (A)having a quaternary ammonium salt group, the copolymerizable monomer (B)having one unsaturated double bond and the copolymerizable monomer (C)having at least two unsaturated double bonds is polymerized, andsubsequently, preferably the copolymerizable monomer (D) having oneunsaturated bond and the copolymerizable monomer (E) having at least twounsaturated double bonds are added and polymerized. Accordingly, thethus-formed copolymer has a graft chain composed of units of thecopolymerizable monomer (D) having one unsaturated double bond, and thisgraft chain increases the compatibility between the synthetic resin asthe substrate and the copolymer imparting antistatic properties andimproves the dispersibility of this copolymer in the substrate resin.Furthermore, the graft chain has a crosslinked portion composed of unitsof the copolymerizable monomer (E) having at least two unsaturateddouble bonds and a residual double bond, and therefore, a semi-IPNstructure is formed with the synthetic resin as the substrate and achemical bonding is formed by graft polymerization to the residualdouble bond, with the result that the surface hardness of the obtainedshaped article is improved and the adhesion between the synthetic resinas the substrate and the copolymer, i.e., the durability of theantistatic properties, is improved.

The amount of the copolymerizable monomer (D) having one unsaturatedbond is 0(exclusive) to 190 parts by weight, more preferably 10 to 190parts by weight, based on 100 parts by weight of the total of themonomers (A), (B) and (C). The amount of the copolymerizable monomer (E)having at least two unsaturated double bonds is 0(exclusive) to 10 partsby weight, more preferably 0.01 to 10 parts by weight, based on 100parts by weight of the total of the monomers (A), (B) and (C).

Where the synthetic resin as the substrate is a polymer composed mainlyof methyl methacrylate, preferably a compound of the above-mentionedgeneral formula (II) in which n is 2 to 500 is used as thecopolymerizable monomer (B) having one unsaturated bond, a compound ofthe above-mentioned general formula (II) in which n is 0, especiallymethyl methacrylate, is used as the copolymerizable monomer (D) havingone unsaturated double bond, and allyl methacrylate or allyl acrylate isused as the copolymerizable monomers (C) and (E) having at least twounsaturated bonds.

The copolymer imparting antistatic properties in the present inventionis obtained by polymerizing 100 parts by weight of a monomer mixturecomprising more than 20% by weight of the monomer (A) having aquaternary ammonium salt group, 0(exclusive) % to 79.99 (exclusive) % byweight of the copolymerizable monomer (B) having one unsaturated doublebond and 0.01 to 10% by weight of the copolymerizable monomer (C) havingat least two unsaturated double bonds and subsequently, adding andpolymerizing 0(exclusive) to 190 parts by weight of the copolymerizablemonomer (D) having one unsaturated double bond and 0(exclusive) to 10parts by weight of the copolymerizable monomer (E) having at least twounsaturated double bonds. Preferably, the proportions of the respectivemonomers is such that the amount of the monomer (A) having a quaternaryammonium salt group is more than 20% by weight but not more than 70% byweight, the sum of the copolymerizable monomers (B) and (D) having oneunsaturated double bond is 20 to 79.9% by weight, and the sum of thecopolymerizable monomers (C) and (E) having at least two unsaturateddouble bonds is 0.1 to 10% by weight.

If the amount of the monomer (A) having a quaternary ammonium salt groupis not more than 20% by weight, good antistatic properties are notalways obtained, if the sum of the copolymerizable monomers (B) and (D)having one unsaturated double bond is smaller than 20% by weight, theshapeability may be poor; if the sum of the copolymerizable monomers (C)and (E) having at least two unsaturated double bonds is smaller than0.1% by weight, good surface hardness and good durability of antistaticproperties cannot be always given to the obtained shaped article; and ifthe sum of the monomers (C) and (E) exceeds 10% by weight, it isdifficult to coat the copolymer imparting antistatic propertiesuniformly on the casting mold. Use of the monomers (D) and (E) ispreferable for stabilizing the durable antistatic properties and thesurface hardness.

The main reason why the shaped article of the present invention hasdurable antistatic properties is that the copolymer imparting antistaticproperties is integrated with the synthetic resin as the substrate. Morespecifically, the copolymer is swollen with the starting material forthe synthetic resin as the substrate at the step of polymerizing thisstarting material, and in this state, the polymerization of the startingmaterial is advanced to form an integrated layer of the copolymerimparting antistatic properties to the surface of the synthetic resin asthe substrate of the shaped article obtained by the polymerization.Accordingly, the antistatic properties imparted by the invention are notlost by water washing or friction, and in this point, the antistaticproperties imparted by the present invention are advantageous over theantistatic properties given by the customary method of coating a surfaceactive agent on the surface of a shaped article. Moreover, in thepresent invention, since the copolymer imparting antistatic propertiesis present only in the surface portion, good antistatic properties canbe obtained by even a small amount of the copolymer.

The kind of the synthetic resin to be used as the substrate in thepresent invention is not particularly critical, but in the presentinvention, the starting material for the synthetic resin must be used.By the term "starting material" used herein, we mean a material suchthat the polymerization degree and/or the property of the material canbe changed by a reaction such as polymerization. For example, a polymermixture or a polymer/monomer mixture or a monomer mixture can be used.Namely, any of starting materials can be used, as long as thepolymerization degree and/or the property is changed by polymerization,crosslinking or another reaction. More specifically, there can bementioned methyl methacrylate, styrene, other radical-polymerizablemonomers, mixtures and polymers thereof, a polyol/polyisocyanatemixture, a mixture of an oligomer having epoxy groups at both of theterminals with a polyamine or polyamide, an unsaturated polyester, anovolak polymer/bisoxazoline mixture, a reactive silicone rubberoligomer, and a polycarbonate cyclic oligomer.

A methacrylic resin formed by using methyl methacrylate, a monomermixture comprising at least 50% by weight of methyl methacrylate and upto 50% by weight of at least one monomer copolymerizable therewith or apartial polymerization product thereof as the starting material isespecially preferable as the synthetic resin to be used as the substratein the present invention.

As the monomer copolymerizable with methyl methacrylate, there can bementioned methacrylic acid esters such as ethyl methacrylate, butylmethacrylate and 2-ethylhexyl methacrylate, acrylic acid esters such asmethyl acrylate, ethyl acrylate, butyl acrylate and 2-ethylhexylacrylate, unsaturated carboxylic acids such as acrylic acid, methacrylicacid, maleic acid and itaconic acid, acid anhydrides such as maleicanhydride and itaconic anhydride, maleimide derivatives such asN-phenylmaleimide, N-cyclohexylmaleimide and N-t-butylmaleimide,hydroxyl group-containing monomers such as 2-hydroxyethyl acrylate,2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate and2-hydroxypropyl methacrylate, nitrogen-containing monomers such asacrylamide, methacrylamide, diacetone acrylamide and dimethylaminoethylmethacrylate, epoxy group-containing monomers such as allyl glycidylether, glycidyl acrylate and glycidyl methacrylate, styrene typemonomers such as styrene and α-methylstyrene, and crosslinking agentssuch as ethylene glycol diacrylate, allyl acrylate, ethylene glycoldimethacrylate, allyl methacrylate, divinylbenzene andtrimethylolpropane triacrylate, although the copolymerizable monomersthat can be used are not limited to those exemplified above.

The kind and amount of the copolymerizable monomer can be determinedaccording to the intended synthetic resin shaped article.

Additives such as a colorant, a release agent, an ultraviolet absorber,a heat stabilizer, and a filler can be incorporated into the startingmaterial for the synthetic resin as the substrate in the presentinvention.

As the casting mold to be used in the present invention, there can bementioned casting molds composed of an inorganic glass such as areinforced glass, a metal such as stainless steel, aluminum or chromiumplating, or a resin such as a polyester resin. The surface of a castingmold of a glass or metal is generally a mirror surface, but a castingmold having a surface delustered by forming a multiplicity of fineprotrusions thereon can be used when necessary.

As the means for forming a film of the copolymer imparting antistaticproperties on the surface of the casting mold, a method of coating thecopolymer in the form of a solution in water and/or an organic solventis simple and preferable.

Components such as a release agent, a defoaming agent, a leveling agent,a monomer, and a crosslinking agent can be added to the solution ormixture of the copolymer, as long as the antistatic properties of theformed film, the polymerizability of the starting material for thesynthetic resin as the substrate, and the physical properties of thesubstrate resin are not adversely affected.

As the means of coating the solution or mixture of the copolymer on thesurface of the casting mold, there can be mentioned spray coating, flowcoating, bar coating, and dip coating.

Where a plate-like methacrylic resin shaped article is preparedaccording to the present invention, from the industrial viewpoint it ispreferable to adopt a continuous casting process using, as the castingmold, two confronting stainless steel endless belts having onemirror-polished surface and moved at the same speed in the samedirection, and gaskets, as illustrated in FIG. 1.

The present invention will now be described in detail with reference tothe following examples that by no means limit the scope of theinvention.

The electric properties of all of the samples were determined after aone day conditioning at a temperature of 20° C. and a relative humidityof 65%. The charge half-value time was measured under the conditions ofan applied voltage of 10,000 V, a sample-rotating speed of 1,550 rpm, anapplication time of 30 seconds, a measurement temperature of 20° C., anda measurement relative humidity of 65%, using a static honest meter(supplied by Shishido Shokai), wherein the sample voltage at the time ofapplication of the voltage was designated as the initial voltage (V),and the time required for reducing the sample voltage to 1/2 of theinitial voltage after application of the voltage was designated as thecharge half-value time (sec).

The surface resistivity (Ω) was measured at a measurement temperature of20° C. and a measurement relative humidity of 65% under an appliedvoltage of 500 V 1 minute after the application of the voltage, using anhigh megohm meter (Model TR-8601 supplied by Takeda-Riken). Each sampleplate was cut to a size of 40 mm×40 mm and the cut piece was wiped 60times with gauze in running water, and the surface resistivity (Ω) afterthe water washing was measured by the above-mentioned high megohm meter.

The surface hardness was determined according to the pencil scratch testof JIS K-5400 (usual paint test methods), and the transparency wasevaluated based on the haze value determined by an integration ball-typehaze meter (Model SEP-H-SS supplied by Nippon Seimitsu Kogaku).

EXAMPLE 1

A glass flask equipped with stirring vanes was charged with 112.2 partsby weight of diethylaminoethyl methacrylate and 220 parts by weight ofmethanol, and a mixture of 75.7 parts by weight of dimethyl sulfate and40 parts by weight of methanol was added dropwise with stirring so thatthe inner temperature was kept below 30° C. After the dropwise addition,the mixture was stirred for 30 minutes to form a solution of a monomer(M-1) having a quaternary ammonium salt group.

To this solution were added 3 parts by weight of azobisisobutyronitrile,2.5 parts by weight of n-octylmercaptan, 243 parts by weight ofmethanol, 249.1 parts by weight of polyethylene glycol(23)monomethacrylate monomethyl ether (the parenthesized value indicates thenumber of ethylene glycol units in the polyethylene glycol), and 9.4parts by weight of allyl methacrylate, and polymerization was carriedout for 1 hour at 60° C. in a nitrogen atmosphere. Subsequently, 186.8parts by weight of methyl methacrylate and 9.4 parts by weight of allylmethacrylate were added to the reaction mixture, and polymerization wasconducted for 5 hours at 60° C. in a nitrogen atmosphere to obtain asolution of a copolymer (P-1) imparting antistatic properties.

A film-forming starting material was formed by dissolving 5% by weightof the solution of the copolymer (P-1) in 95% by weight of methanol andthis starting material was spray-coated and dried on the mirror surfaceof a stainless steel sheet having a length of 600 mm, a width of 450 mm,and a thickness of 3 mm and having one surface mirror-polished. Acasting mold was assembled by using two of the thus-treated stainlesssteel sheets and gaskets so that the thickness of the formed sheet was 3mm. A starting material for a synthetic resin, formed by dissolving 0.05part by weight of 2,2'-azobisisobutyronitrile as the polymerizationinitiator in 100 parts by weight of a partial polymerization product ofmethyl methacrylate (viscosity =1,000 cP at 20° C., polymerizationdegree=20%) and removing dissolved air by reducing the pressure, wascast into the casting mold. Polymerization was carried out for 10 hoursat 60° C. and for 4 hours at 110° C., the temperature was dropped tonormal temperature, and the shaped article was released from the mold.The surface resistivity of the methacrylate resin plate was 1.2×10¹⁰ ,the charge half-value time was 1 second, and the haze value was 1.0%.

The obtained plate was subjected to the water-washing treatment, and theantistatic properties were immediately evaluated. It was found that thesurface resistivity was 9.5×10⁹ Ω and the charge half-value time was 1second. When determined according to the pencil scratch test of JISK-5400, it was found that the surface hardness was 3H.

COMPARATIVE EXAMPLE 1

A methacrylic resin plate having a thickness of 3 mm was prepared in thesame manner as described in Example 1 except that stainless steelmirror-surface sheets not treated with the antistatic polymer were used.

The surface resistivity of the obtained plate was higher than 10¹⁶ Ω,the charge half-value time was more than 120 seconds, the haze value was1.0%, and the surface hardness was 3H.

EXAMPLES 2 THROUGH 13

Copolymers (P-2) through (P-13) having a composition shown in Table 2were prepared in the same manner as in Example 1 by using as the monomer(A) the same monomer (M-1) as used in Example 1, or a monomer (M-2),(M-3), (M-4) or (M-5) having a quaternary ammonium salt group, whichwere prepared from a combination of an amino group-containing acrylateor methacrylate and a quaternizing agent, shown in Table 1, in the samemanner as in Example 1.

Methacrylic resin plates having a thickness of 3 mm were prepared fromthese copolymers in the same manner as described in Example 1.

The evaluation results are shown in Table 2.

COMPARATIVE EXAMPLES 2 THROUGH 4

Copolymers (P-14), (P-15) and (P-16) having a composition shown in Table2 were prepared by using the solution of the monomer (M-1), andmethacrylic resin plates having a thickness of 3 mm were obtained in thesame manner as described in Example 1 by using these copolymers. Theevaluation results are shown in Table 2.

From the results obtained in Comparative Examples 2 and 3 it is seenthat, if the copolymerizable monomers (C) and (E) having at least twounsaturated double bonds are not used, the surface hardness of theshaped article is lowered.

From the results obtained in Comparative Example 4 it is seen that, ifthe amount of the monomer (A) having a quaternary ammonium salt group inthe copolymer is not more than 20% by weight, good antistatic propertiescannot be imparted.

                  TABLE 1                                                         ______________________________________                                                   Amine-Containing                                                   Monomer    Acrylate or    Quaternizing                                        (A)        Methacrylate   Agent                                               ______________________________________                                        M-2        Dimethylaminoethyl                                                                           Diethyl sulfate                                                methacrylate                                                       M-3        Dimethylaminoethyl                                                                           Methyl p-toluene-                                              methacrylate   sulfonate                                           M-4        Dimethylaminoethyl                                                                           Methyl chloride                                                methacrylate                                                       M-5        Dimethylaminoethyl                                                                           Dimethyl sulfate                                               acrylate                                                           ______________________________________                                    

                                      TABLE 2                                     __________________________________________________________________________            Composition of copolymer                                                      First stage                   Second stage                                    Monomer                                                                             Monomer          Monomer                                                                              Monomer          Monomer                Co-     (A)   (B)              (C)    (D)              (E)                         poly- ratio    ratio   ratio  ratio   ratio    ratio   ratio                  mer   (%)      (%)     (%)    (%)     (%)      (%)     (%)               __________________________________________________________________________    Example                                                                       No.                                                                           2    P-2                                                                              M-1                                                                              29 PEG (500)                                                                           39 --   -- AMA 1.5                                                                              MMA  29 --    -- AMA  1.5               3    P-3                                                                              M-1                                                                              29  --   -- MMA  29 AMA 1.5                                                                              --   -- PEG (23)                                                                            39 AMA  1.5               4    P-4                                                                              M-1                                                                              29 PEG (23)                                                                            19.5                                                                             MMA  14.5                                                                             AMA 1.5                                                                              MMA  14.5                                                                               "   19.5                                                                             AMA  1.5               5    P-5                                                                              M-1                                                                              29   "   19.5                                                                             HEMA 14.5                                                                             AMA 1.5                                                                              HEMA 14.5                                                                               "   19.5                                                                             AMA  1.5               6    P-6                                                                              M-1                                                                              49   "   24 --   -- AMA 1.5                                                                              MMA  24 --    -- AMA  1.5               7    P-7                                                                              M-1                                                                              24   "   24 --   -- AMA 1.5                                                                              MMA  49 --    -- AMA  1.5               8    P-8                                                                              M-1                                                                              68   "   14.5                                                                             --   -- AMA 1.5                                                                              --   -- PEG (23)                                                                            14.5                                                                             AMA  1.5               9    P-9                                                                              M-1                                                                              29.5                                                                               "   39.2                                                                             --   -- AMA 1.5                                                                              MMA  29.5                                                                             --    -- EDMA 0.3               10   P-10                                                                             M-2                                                                              34   "   34 --   -- AMA 1.5                                                                              MMA  29 --    -- AMA  1.5               11   P-11                                                                             M-3                                                                              29   "   39 --   -- AMA 1.5                                                                              MMA  29 --    -- AMA  1.5               12   P-12                                                                             M-4                                                                              29   "   39 --   -- AMA 1.5                                                                              MMA  29 --    -- AMA  1.5               13   P-13                                                                             M-5                                                                              29   "   39 --   -- AMA 1.5                                                                              MMA  29 --    -- AMA  1.5               Compar-                                                                       ative                                                                         Example                                                                       2    P-14                                                                             M-1                                                                              30 PEG (23)                                                                            40 --   -- --  -- MMA  30 --    -- --   --                3    P-15                                                                             M-1                                                                              30   "   40 MMA  30 --  -- --   -- --    -- --   --                4    P-16                                                                             M-1                                                                              15   "   15 MMA  68 AMA 2  --   -- --    -- --   --                __________________________________________________________________________                                            Evaluation results                                                            surface                                                                             resistivity                                                                           surface                                                         initial                                                                             water-washing                                                                         hardness                                                        (Ω)                                                                           (Ω)                                                                             (pencil                 __________________________________________________________________________                                                          hardness)                                                  Example                                                                       No.                                                                           2    8.6 × 10.sup.9                                                                1.2 × 10.sup.9                                                                  3H                                                         3    2.2 × 10.sup.10                                                               1.5 × 10.sup.10                                                                 2H                                                         4    1.7 × 10.sup.10                                                               1.0 × 10.sup.10                                                                 3H                                                         5    8.8 × 10.sup.9                                                                8.0 × 10.sup.9                                                                  3H                                                         6    6.5 × 10.sup.9                                                                7.2 × 10.sup.9                                                                  3H                                                         7    8.3 × 10.sup.11                                                               6.3 × 10.sup.11                                                                 3H                                                         8    1.3 × 10.sup.9                                                                2.5 × 10.sup.9                                                                  2H                                                         9    9.5 × 10.sup.9                                                                9.2 × 10.sup.9                                                                  3H                                                         10   5.2 × 10.sup.10                                                               4.1 × 10.sup.10                                                                 3H                                                         11   4.3 × 10.sup.10                                                               3.5 ×                                                                           3H.sup.10                                                  12   7.5 × 10.sup.9                                                                7.2 × 10.sup.9                                                                  3H                                                         13   9.2 × 10.sup.9                                                                8.7 × 10.sup.9                                                                  3H                                                         Compar-                                                                       ative                                                                         Example                                                                       2    1.3 × 10.sup.10                                                               2.4 × 10.sup.10                                                                 2B                                                         3    1.6 × 10.sup.10                                                               2.2 × 10.sup.10                                                                 2B                                                         4    4.5 × 10.sup.14                                                               6.3 × 10.sup.14                                                                 3H                      __________________________________________________________________________     Note                                                                          %: % by weight                                                                PEG (500): polyethylene glycol (500) monomethacrylate monomethyl ether        PEG (23): polyethylene glycol (23) monomethacrylate monomethyl ether          MMA: methyl methacrylate                                                      HEMA: 2hydroxyethyl methacrylate                                              AMA: allyl methacrylate                                                       EDMA: ethylene glycol dimethacrylate                                     

Each parenthesized number indicates the number of ethylene glycol unitsin polyethylene glycol.

EXAMPLE 14

A methacrylic resin plate having a thickness of 3 mm was prepared in thesame manner as described in Example 1 except that a reinforced glasssheet having a length of 600 mm, a width of 450 mm, and a thickness of 6mm was used for the casting mold.

The surface resistivity of the resin plate was 7.2×10⁹ Ω, the chargehalf-value time was 1 second, the haze value was 1.0%, and the surfacehardness was 3H.

The surface resistivity after water washing was 6.5×10⁹ Ω, and thecharge half-value time after water washing was 1 second.

EXAMPLE 15

A methacrylic resin plate having a thickness of 3 mm was prepared in thesame manner as described in Example 1 except that a laminate of astainless steel sheet having a length of 600 mm, a width of 450 mm, anda thickness of 3 mm, and a polyester film having a thickness of 250 μm(Luminor, standard type, supplied by Toray) adhered on the stainlesssteel sheet was used for the casting mold.

The surface resistivity of the resin plate was 8.5×10⁹ Ω, the chargehalf-value time was 1 second, and the surface hardness was 3H.

The surface resistivity after water washing was 8.6× 10⁹ Ω, and thecharge half-value time after water washing was 1 second.

EXAMPLE 16

An apparatus for the continuous production of a methacrylic resin plate,as shown in FIG. 1 was used as the casting mold.

Referring to FIG. 1, belts 1 and 1' having a width of 1.5 m and athickness of 1 mm, and having one surface mirror-polished, weretravelled at a speed of 2 m/min by driving a main pulley 2'. An initialtension on the belts was given by arranging a hydraulic cylinder onpulleys 2 and 2', and was set at 10 kg/mm² of the belt section. Eachreference numeral 3 and 3' represents a pulley.

A film-forming starting material 5,5' comprising 1.0% by weight ofcopolymer (P-1), 98.0% by weight of methyl methacrylate and 1.0% byweight of methanol was coated on the mirror surfaces of the belts 1 and1' by roll coaters 6 and 6'.

The thus-treated belts were arranged to confront each other and bothside portions thereof were sealed by gaskets in the form of pipes 15composed of plasticized polyvinyl chloride. A starting material 14 for asynthetic resin as the substrate, which comprised 100 parts by weight ofa partial polymerization product of methyl methacrylate (the content ofthe polymer having an average polymerization degree of 1,800 was 21% byweight), 0.05 part by weight of 2,2'-azobis(2,4-dimethylvaleronitrile),and 0.01 part by weight of Tinuvin P was cast in the space between thebelts through a casting device by a metering pump.

The entire length of the polymerization zone was 96 m. In the formerportion having a length of 66 m, the distance between the surfaces ofthe belts was regulated by idle rollers 4 and 4' arranged at intervalsof 15 cm, and warm water maintained at 80° C. was sprayed and scatteredthrough nozzles from the outer surfaces of the belts to heat thestarting material. In the latter portion having a length of 30 m, thebelts were supported by idle rollers arranged at intervals of 1 m, andthe material between the belts was heated to about 130° C. by aninfrared ray heater 17 and the obtained product was cooled and thenseparated from the belts. In this manner, a methacrylic resin sheethaving a thickness of 3 mm was continuously prepared.

The surface resistivity of the obtained resin sheet was 1.5×10¹⁰ Ω, thecharge half-value time was 1 second, the haze value was 1.0%, and thesurface hardness was 3H. The surface resistivity after water washing was9.8×10⁹ Ω, and the charge half-value time after water washing was 1second.

COMPARATIVE EXAMPLE 5

A methacrylic resin plate having a thickness of 3 mm was prepared in thesame manner as described in Example 1 except that a laminate formed byadhering a polyester film onto the surface of a stainless steel sheethaving a length of 600 mm, a width of 450 mm, and a thickness of 3 mmwas used for the casting mold and the copolymer obtained in ComparativeExample 3 was used as the copolymer imparting antistatic properties.

The surface resistivity of the obtained resin sheet was 7.8×10⁹ Ω, andthe surface hardness was 2B. After water washing, the surface resistancevalue was 3.5×10¹³ Ω. From these results, it is seen that if thecopolymerizable monomers (C) and (E) having at least two unsaturateddouble bonds are not used, a good resistance to water washing, i.e., agood durability of the antistatic properties, cannot be imparted.

As apparent from the foregoing description, according to the presentinvention, a synthetic resin shaped article having good and durableantistatic properties with no lowering of the inherent physicalproperties of the synthetic resin, and a process for the preparation ofthis synthetic resin shaped article, are provided, and the occurrence ofantistatic problems arising when synthetic resins are utilized, can beprevented.

We claim:
 1. A process for the preparation of a synthetic resin-shapedarticle having good antistatic properties, which comprises:a)polymerizing 100 parts by weight of a monomer mixture comprising (A)more than 20% by weight of a monomer having a quaternary ammonium saltgroup, which is represented by the following formula (I): ##STR4##wherein R₁ represents a hydrogen atom or a methyl group; R₂, R₃ and R₄each represents a hydrogen atom or an alkyl group having 1 to 9 carbonatoms; m is an integer from 1 to 10; and X represents an anion of aquaternizing agent; (B) less than 79.99% by weight of a copolymerizablemonomer having one unsaturated double bond; and (c) 0.01 to 10% byweight of a copolymerizable monomer having at least two unsaturateddouble bonds, to prepare a copolymer (b) comprising the units derivedfrom the monomers (A), (B) and (C); b) subsequently polymerizing (D) 0(exclusive) to 190 parts by weight of a copolymerizable monomer havingone unsaturated double bond and (E) 0 (exclusive) to 10 parts by weightof a copolymerizable monomer having at least two unsaturated doublebonds in the presence of 100 parts by weight of the copolymer (b), toprepare a copolymer (a); c) forming a film of the copolymer (a) on themolding surface of a casting mold; and d) supplying a starting materialcapable of forming a synthetic resin into the casting mold andpolymerizing the starting material to form the substrate in the castingmold, thereby transferring the film of step c) to the surface of thesubstrate from the molding surface of the casting mold.
 2. The processfor the preparation of a synthetic resin shaped article according toclaim 1, wherein the monomer (D) is used in an amount of 10 to 190 partsby weight and the monomer (E) is used in an amount of 0.01 to 10 partsby weight.
 3. The process for the preparation of a synthetic resinshaped article according to claim 1, wherein at least one of thecopolymerizable monomers (B) and (D) having one unsaturated double bondis the same as the monomer constituting the synthetic resin as thesubstrate or a monomer capable of forming a resin having a goodcompatibility with the synthetic resin as the substrate.
 4. The processfor the preparation of a synthetic resin shaped article according toclaim 1, wherein the starting material for the synthetic resin as thesubstrate is methyl methacrylate, a monomer mixture comprising at least50% by weight of methyl methacrylate and up to 50% by weight of at leastone monomer copolymerizable therewith, or a partial polymerizationproduct thereof.
 5. The process for the preparation of a synthetic resinshaped article according to claim 1, wherein the copolymerizablemonomers (B) and (D) having one unsaturated double bond are selectedfrom compounds represented by the following general formula (II):##STR5## wherein R₅ represents a hydrogen atom or a methyl group, R₆represents a hydrogen atom or an alkyl, aryl or aralkyl group having 1to 18 carbon atoms, A represents an alkylene group having 2 to 4 carbonatoms, and n is an integer of from 0 to
 500. 6. The process for thepreparation of a synthetic resin shaped article according to claim 5,wherein n in the formula (II) is an integer of from 2 to
 500. 7. Theprocess for the preparation of a synthetic resin shaped articleaccording to claim 1, wherein the copolymerizable monomers (C) and (E)having at least two unsaturated double bonds are compounds in which atleast one of the functional groups is an allyl group, a methallyl group,a vinyl group, a vinylidene group or a vinylene group.
 8. The processfor the preparation of a synthetic resin shaped article according toclaim 1, wherein the anion of the quaternizing agent of the monomer (A)having a quaternary ammonium salt group, represented by the generalformula (I), is represented by the formula R₇ SO₃ ⁻ or R₇ OSO₃ ⁻ inwhich R₇ represents a hydrogen atom or an alkyl group having 1 to 20carbon atoms, which may contain a phenyl group.
 9. The process for thepreparation of a synthetic resin shaped article according to claim 1,wherein the copolymerizable monomer (B) having one unsaturated doublebond is a compound represented by the following general formula (II):##STR6## wherein R₅ represents a hydrogen atom or a methyl group, R₆represents a hydrogen atom or an alkyl, aryl or aralkyl group having 1to 18 carbon atoms, A represents an alkylene group having 2 to 4 carbonatoms, and n is an integer of from 2 to 500;the copolymerizable monomer(D) having one unsaturated double bond is methyl methacrylate; and thecopolymerizable monomers (C) and (E) having at least two unsaturateddouble bonds are allyl methacrylate or allyl acrylate.
 10. The processfor the preparation of a synthetic resin shaped article according toclaim 1, wherein the film of the copolymer(a) is formed on the moldingsurface of the mold by coating the molding surface with a solution ofthe copolymer(a) in a medium selected from the group consisting of waterand organic solvents.
 11. The process for the preparation of a syntheticresin shaped article according to claim 1, wherein the casting moldcomprises two confronting stainless steel endless belts moving at thesame speed in the same direction, each endless belt having one surfacemirror-polished, and gaskets.